1. Field of the Invention
The present invention relates to a novel process for the production of oligomers of normal olefins of C.sub.2 to C.sub.10 carbon atoms and in particular C.sub.8 olefins by the dimerization of n-butenes.
2. Prior Art
The reaction of olefins to form longer chains of two or more monomer units is well known. It is well known that ethylene and other olefins can be polymerized to form relatively low molecular weight products through the use of certain organo-metallic catalyst. Broadly, these catalysts are compounds of metals of groups IV to VI of the Periodic Table of elements in combination with other compounds of metals of groups I to III. The Ziegler catalysts are representatives of such catalysts and are preferably specific combinations of titanium halide and a trialkyl aluminum component, with or without other metal promoters. Other catalysts such as alkyl aluminum halides (preferably the chloride) in combination with alkyl titanium esters have also been used to carry out this reaction.
These catalysts are homogeneous in that they are soluble in the reaction medium. The catalysts are very effective, that is the reaction can easily be carried out to produce high molecular weight compounds, with the appropriate amounts of catalyst. In some instances, by using extremely low concentrations of catalyst in the reaction system, low molecular weight products may be produced, in particular dimers, trimers and tetramers.
Free radicals, carbonium ions and carbanions have also been used to promote the reaction of olefins, particularly alpha-olefins to produce polymers of high molecular weight.
The use of acid catalysts such as sulfuric acid to selectively react isoolefins in the presence of other olefins to produce lower molecular weight products, e.g., U.S. Pat. Nos. 3,564,317 and 3,832,418 is also well known. U.S. Pat. No. 4,065,512 discloses the use of perfluorosulfonic acid resin, particularly in the form of films for the polymerization of isobutene to produce dimers, trimers and higher oligomers.
More recently, U.S. Pat. No. 4,215,011 disclosed the use of acid cation exchange resin in a heterogenous combination reaction-distillation system for the selective dimerization of isobutene in the presence of normal butenes. The reaction is highly preferential for the reaction of isobutene with itself, although some codimer between n-butenes and isobutene are formed, and provides a means to separate isobutene from a C.sub.4 stream.
It would appear from the art that normal butenes are not reactive, other than with isobutene in the presence of acid catalyst or acid cation exchange resin.